In recent years, IETF (Internet Engineering Task Force) has been considering an IP mobility scheme for seamless movement, which enables handover between a plurality of different wireless communication networks, such as a mobile phone network, a wireless LAN and the likes, in order to achieve ubiquitous environment. As a specific protocol of the IP mobility scheme, there are Mobile IPv4 and Mobile IPv6 (which are correctively referred to as Mobile IP, hereinafter. See Non-Patent Document 1) for supporting movement of individual communication terminal, and NEMO (Network Mobility) for supporting mobility of a network as a unit.
In Mobile IP and NEMO, when a mobile node (hereinafter, abbreviated as MN) performs handover from a wireless communication network (hereinafter, referred to as “first wireless NW”) of a handover source to another wireless communication network (a wireless communication network of a handover destination), the MN registers an IP address of the wireless communication network of the handover destination (hereinafter, referred to as “second wireless NW”) as a care-of address (hereinafter, referred to as “CoA”) with a home agent (hereinafter, referred to as “HA”) to which the MN belongs. Thereby, the MN can communicate with a correspondent node (hereinafter, referred to as “CN”) as a communication counterpart via the second wireless NW.
As handover methods, there are known MBB (Make-Before-Break) method to connect to the second wireless NW before disconnecting the first wireless NW and BBM (Break-Before-Make) method to connect to the second wireless NW after disconnecting the first wireless NW. The BBM method has an advantage to be able to perform handover in relatively simple processing, as having no necessity to administrate simultaneous connection to a plurality of wireless communication networks.
Non-Patent Document 1: C. Perkins, “IP Mobility Support (RFC2002)”, [online], October 1996, IETF, [searched on Mar. 15, 2006], internet <URL: http://www.ietf.org/rfc/rfc2002.txt